SNM used to define virtual_alias_maps in extraConfig which collides with
the same parameter defined by the standard services.postfix.virtual
option. This led to *lots* of warnings during postfix startup like
```
May 02 18:29:58 nun postfix/master[24758]: warning: /etc/postfix/main.cf, line 47: overriding earlier entry: virtual_alias_maps=hash:/etc/postfix/virtual
```
Refraining from overriding virtual_alias_maps has the additional
advantage that virtual aliases defined by other modules dont' stop
working with SNM.
It seemed weird to me that preStart on postfix was used to generate
files not needed directly by postfix and for the self-signed
certificate which is also needed by dovecot. nginx.service was also
used as a proxy for when ACME certificate generation was done.
So I have created mailserver-certificates.target for when certificates
are available for other services. For self-signed that means that a
new oneshot service called mailserver-selfsigned-certificate has been
run. And for ACME this means that the target
acme-selfsigned-certificates has been reached (which is when acme has
created the self-signed certificates used before the actual
certificates provided by LetsEncrypt are created). This setup has the
added bonus that if you want to run a service to provide your own
certificates you can set that to run before
mailserver-certificates.target.
DH Parameters are only needed by dovecot so generation of that file has
been moved to the dovecot2 preStart.
And lastly the only remaining reason to for dovecot to start before
postfix was that the auth and lmtp sockets where located in a directory
created by postfix. But since they could just as well be located in
/run/dovecot2 as long as postfix has access to them I have moved them
there.
The dh.pem file is currently created by the postfix prestart
script. If the entropy of the system is to low, the postfix prestart
can timeout. In this case, an empty file is created.
If the user restarts the postfix service, the dh.pem is not created
because the file already exists (but is empty).
When a ssl is established with dovecot, it fails with this message:
imap-login: `Error:Failed to initialize SSL server context: Couldn't parse DH parameters:
error:0906D06C:PEM routines:PEM_read_bio:no start line: Expecting: DH
PARAMETERS`
With this patch, the postfix service creates the dh.pem if the dh.pem
doesn't exist or if it is empty. It doesn't fix the entropy or
timeout issue but at least, the user knows something is failing:/
